(a) Field of the Invention
The present disclosure relates to display devices, and, more particularly, to an organic light emitting diode (OLED) display and a manufacturing method thereof.
(b) Discussion of the Related Art
With the demand for lightweight and thin monitors or televisions liquid crystal displays (“LCDs”) are being substituted for conventional cathode ray tubes (“CRTs”).
However, since the LCD is a light receiving/emitting device, the LCD requires a backlight, and may have a slow response speed and limited viewing angle as compared with the conventional CRT.
In recent years, an OLED display has attracted attention as a display device due to its faster response speed and wider viewing angle.
The OLED display includes two electrodes and a light emitting layer positioned therebetween. Electrons injected from one electrode and holes injected from the other electrode are combined in the light emitting layer so as to form excitons, and the excitons emit light through energy emission.
Since the OLED display is a self-emitting type, it does not need an additional light source. Therefore, the OLED display has low power consumption, as well as excellent response speed, viewing angle, and contrast ratio.
An OLED display can be classified as a passive matrix OLED display and an active matrix OLED display according to its driving mode.
Among these, an active matrix OLED display has a structure in which electrodes and a light emitting layer are on a thin film transistor display panel, and the thin film transistor display panel includes signal lines, a switching thin film transistor connected to the signal lines that controls a data voltage, and a driving thin film transistor that flows a current into a organic light emitting device by supplying the data voltage received from the switching thin film transistor as a gate voltage.
A semiconductor constituting the channel layer of the thin film transistor of the OLED display may have its characteristics changed during a photolithography process for forming another thin film, and such a change of characteristics of the semiconductor may deteriorate the performance of the thin film transistor.
An oxide semiconductor can be used for the semiconductor constituting the channel layer of the thin film transistor of the OLED display. When an oxide semiconductor is used, the characteristics of the semiconductor layer may deteriorate due to light. Thus, it is important to block external light.
Further, when forming a thin film transistor, an organic light emitting element, and thin film layers such as an anode and a cathode of an OLED display, a photolithography process is used involving a mask. As the number of masks used in each photolithography process increases, the manufacturing process becomes complicated and the manufacturing cost increases. Therefore, in order to improve the productivity of OLED displays, it becomes desirable to form a thin film layer using a smaller number of masks.